Cardiac arrhythmias can generally be thought of as disturbances of the normal rhythm of the heart muscle. Cardiac arrhythmias are broadly divided into two major categories, bradyarrhythmia and tachyarrhythmia. Tachyarrhythmia can be broadly defined as an abnormally rapid heart (e.g., over 100 beats/minute, at rest), and bradyarrhythmia can be broadly defined as an abnormally slow heart (e.g., less than 50 beats/minute). Tachyarrhythmias are further subdivided into two major sub-categories, namely, tachycardia and fibrillation. Tachycardia is a condition in which the electrical activity and rhythms of the heart are rapid, but organized. Fibrillation is a condition in which the electrical activity and rhythm of the heart are rapid, chaotic, and disorganized. Tachycardia and fibrillation are further classified according to their location within the heart, namely, either atrial or ventricular.
In general, atrial arrhythmias are non-life threatening, chronic conditions, because the atria (upper chambers of the heart) are only responsible for aiding the movement of blood into the ventricles (lower chambers of the heart), whereas ventricular arrhythmias are life-threatening, acute events, because the heart's ability to pump blood to the rest of the body is impaired if the ventricles become arrhythmic.
Current treatments for atrial fibrillation include drug, external cardioversion, ablation, and pacing therapy. Each of these treatments has positive and negative aspects. For example, often times side effects associated with drug therapy can lead to low compliance among the patient population. Additionally, most times a patient can be converted to normal sinus rhythm using external cardioversion. However, many times the patients tend to revert back to atrial fibrillation. This can also be the case with ablation therapy. Pacing therapy is currently being clinically investigated to ascertain its applicability as a valid therapy for atrial fibrillation. There are subsets of patients in whom pacing therapy is effective in preventing or reducing the incidence of paroxysmal atrial fibrillation and/or stabilizing the rhythm after pharmacologic therapy or cardioversion has been successful in terminating an episode of persistent atrial fibrillation.
Internal cardioversion is yet another option for treating atrial tachyarrhythmias such as atrial fibrillation. This option has an advantage in that most times cardioversion is successful, and hospitalization (outpatient and inpatient) is not required. There are existing devices for treating atrial fibrillation using internal cardioversion. In one instance, a patient activates a device to provide shock therapy by simply placing a credit card-like activator over an implanted device. The disadvantage of this type of therapy delivery is that it is patient dependent. In many cases patients who receive uncomfortable shocks are less likely to deliver therapy to themselves since they perceive the pain from the shock to be worse than the side effects of atrial fibrillation.
Other devices can be programmed to provide shocks during a certain times of the day. For example, the device might be programmed to administer therapy to a patient suffering from atrial fibrillation early in the morning when the patient desires to wake up.
Atrial fibrillation is a disease that affects many active people who lead busy lives and often cover several time zones each week, and in some cases each day. For these types of people, their desired “wake-up” time can vary by 6 hours or more within a given time zone. However, programming a device to administer therapy at the same time during a day (e.g. in the early morning waking hours) is not ideal for a patient who changes time zones or whose lifestyle habits are highly variable.
This invention arose out of concerns associated with providing improved methods and systems for administering cardiac therapy to patients, and particularly, to patients who suffer from atrial fibrillation.